1. Technical Field
This invention relates generally to the manufacturing of steel in a furnace and more particularly to the manufacturing of steel from scrap metal in an electric arc furnace using scrap automotive tires as an auxiliary heat supplying source.
2. Description of the Prior Art
Scrap automotive tires present an environmental problem and recycling is practically nonexistent. Tires do not degrade in landfills and when stockpiled, create a major fire hazard that is impossible to extinguish once ignited. Since they have about the same heating value as coke, 15,000 BTU's per pound, a tire weighing about 20 pounds has approximately 300,000 BTU's. The scrap automotive tires are so plentiful that they have a near zero cost. At the present time, scrap automotive tires are being used as fuel or auxiliary fuel in a variety of operations such as cement kilns, coal fired generators and other applications wherein a controlled firing rate is used. In such instances, it is often necessary to shred the scrap automotive tires prior to using in a furnace. Also, when the scrap automotive tires contain steel belts, it is often necessary to remove the steel belts. In some instances whole rubber tires have been used but such use required equipment changes that reduced the cost advantages. In the manufacturing of steel from scrap metal, some of the steel mills add coke or coal to the scrap metal that is melted in a furnace such as an electric arc furnace.
An Electric Arc Furnace (EAF) is not an ordinary furnace in any sense of the word. It is a vessel for melting steel and providing metallurgical processing. It is believed that the EAF is the best choice for use of the tires, or as it is often referred to, tire derived fuel (“TDF”), as it can overcome all of the specific problems associated with the steel belts and beads when using TDF.
Tires are sometimes used as a fuel or supplemental fuel in the generation of electric power. Because of the problems created by the steel in the TDF they are not widely used or accepted as a fuel by electric utilities. Whether or not tires are used, the electric power has to be converted to higher voltages, transmitted to the steel mill and then converted back into heat by the electric arc. By using tires directly as energy in the steel furnace all of the losses in transmission and conversion are eliminated.
Because of the problems created by the steel belts and beads, the amount of tires now being used is not large enough to consume the amount of tires generated each year as scrap. TDF is the largest use for scrap tire disposal but the amount of tires scraped each year far exceeds the number that can be consumed by all of the various outlets combined. A large portion are shredded and buried in landfills. Only the steel industry, as a very large consumer of energy, has the capability to consume tires in an amount approaching that of the rate of disposal. Therefore, it should be noted that not only does the burning of tires for fuel increase the efficiency of the EAF, it also provides a unique solution for disposing of tires in an environmentally sound method. It provides an alternative to wasting and squandering valuable energy at a time when energy is becoming more scarce and costly. Furthermore, even when the steel industry decides to reuse the steel belts from the tires, the tires are stripped or shredded to remove the rubber to access the steel belts. Much of the rubber is then discarded, which provides only a limited solution to the problem of the waste rubber. There is therefore a need for a process which will utilize both the steel and the rubber found in most tires, and which does so in an efficient and productive manner.
In the EAF, coal or coke is added to the scrap charge as a source of chemical energy but also as an additional source of carbon for the steel being manufactured. The addition of rubber reduces or eliminates the need for coal or coke as a carbon source for steel chemistry requirements.
Therefore, an object of the present invention is to provide an improved method of melting scrap metal using scrap rubber.
Another object of the present invention is to provide an improved method of melting scrap metal using scrap rubber which includes the steps of combining a quantity comprising scrap metal containing steel and at least about 0.25 percent by weight of scrap rubber, forming a bundle of the combined scrap metal and scrap rubber, placing the bundle in an electric arc furnace and applying energy to the quantity in the furnace to start the combustion of the scrap rubber to add additional heat for melting the scrap metal containing steel.
Another object of the present invention is to provide an improved method of melting scrap metal using scrap rubber which will use various types of scrap rubber, including chopped, shredded and even whole tires baled and unbaled, both with the steel belt included and without.
Another object of the present invention is to provide an improved method of melting scrap metal using scrap rubber in which the pollution emitted from the steel plant is greatly reduced, because, specifically, when scrap rubber tires are added to the melting steel, the carbon monoxide emissions that normally occur from the arc furnace are greatly reduced.
Another object of the present invention is to provide an improved method of melting scrap metal using scrap rubber which includes a separate burning container for the tires which is in fluid transmission connection with the furnace such that the heat produced by the burning tires in the container is transferable to the furnace without adding impurities caused by the introduction of steel belts from the tires.
Finally, an object of the present invention is to provide an improved method of melting scrap metal using scrap rubber which is safe, efficient and environmentally sound in use.